The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A layered heater typically includes a plurality of functional layers applied on a substrate by layered processes. The plurality of functional layers may include a dielectric layer on the substrate, a resistive heating layer on the dielectric layer, and a protective layer on the resistive heating layer. The materials for the different functional layers and the substrate are carefully chosen to have compatible coefficient of thermal expansion (CTE) to reduce shear stress generated at the joining interfaces at elevated temperatures. The shear stress may cause generation of cracks or delamination at the joining interfaces, resulting in heater failure.
Only a limited number of materials can be used to form the different functional layers by a specific layered process, thereby limiting the selection of materials for the substrate, which should have a CTE matching the CTE of the dielectric layer applied on the substrate or matching the CTE of the heating layer. For example, when alumina ceramic is used to form the dielectric layer, titanium or molybdenum is generally used to form the substrate due to its chemical and CTE compatibility with the alumina ceramic.
The layered heater may need to be joined to a heating target in some applications. For example, the layered heater may be joined to an electrostatic chuck to form a heated electrostatic chuck. However, the limited selection of materials for the substrate makes joining the layered heater to the electrostatic chuck difficult. When the substrate of the layered heater has a CTE that does not match the CTE of the chuck body, the heated electrostatic chuck is likely to fail due to generation of cracks or delamination at the joining interface at elevated temperatures.
Moreover, the heated electrostatic chuck may be bonded to a top of a pedestal layered heater so that the heated electrostatic chuck is disposed at a predetermined height inside a processing chamber. The pedestal is typically made of a metallic material, and is bonded to the substrate of the layered heater, which may be formed of a ceramic material. Similarly, a limited number of materials can be used to form the pedestal due to the compatibility of the metallic materials with the ceramic material.
The limited number of metals may include, for example, molybdenum, titanium, aluminum-silicon alloys and others. Using these materials to form the pedestal may increase manufacturing costs due to difficulty in manufacturing and machining. Moreover, the metal pedestal, which is exposed to processing gases in the processing chamber, may contaminate the wafer to be processed, if the exposed surface of the metal pedestal is not properly treated.